The present invention relates to a cleaning system including a cleaning blade for scraping off matter to be removed from an outer surface of a rotating member.
An image forming apparatus is provided with a photosensitive drum, an intermediate transfer belt, a fuser roller and a cleaning system, for example. A toner image is formed on an outer surface of the photosensitive drum based on an electrostatic latent image which is formed from image data input into the image forming apparatus. The toner image formed on the photosensitive drum is transferred onto the intermediate transfer belt. The toner image transferred onto the intermediate transfer belt is then transferred onto a sheet of printing paper and fused, or fixed, thereto by the fuser roller. The cleaning system removes residual toner left on such rotating members as the photosensitive drum and the intermediate transfer belt to prevent deterioration of image quality in succeeding processes.
FIG. 1 is a structural diagram schematically showing an example of a conventional cleaning system including a cleaning blade 103. As depicted in FIG. 1, an endless belt 101 is mounted over a rigid rotating body (photosensitive drum) 102. As the cleaning blade 103 having flexibility is pressed toward a cylindrical outer surface of the rotating body 102 with the endless belt 101 passing in between, the cleaning blade 103 scrapes off matter to be removed, i.e., residual toner, left on an outer surface of the turning endless belt 101. If the cleaning blade 103 which scrapes across the endless belt 101 turning on the rigid rotating body 102 is an element made of a rigid material, the cleaning blade 103 will damage the endless belt 101. For this reason, the hardness of the cleaning blade 103 is made lower than that of the outer surface of the rotating body 102. Therefore, a tip end of the cleaning blade 103 could be crushed by a pushing force applied thereto against the outer surface of the rotating body 102.
FIGS. 2A to 2D are explanatory diagrams showing how the conventional cleaning system works. Forced in tight contact with the outer surface of the endless belt 101, the cleaning blade 103 scrapes and collects toner powder adhering to the outer surface of the endless belt 101 as shown in FIG. 2A. The tip end of the cleaning blade 103 is pulled in a turning direction (clockwise direction as illustrated) of the rotating body 102 due to a frictional force exerted between the endless belt 101 and the cleaning blade 103 as shown in FIG. 2B. When the frictional pulling force exerted on the cleaning blade 103 by the endless belt 101 in the turning direction of the rotating body 102 exceeds a limit of buckling strength of the cleaning blade 103, the tip end of the cleaning blade 103 bounces back due to its resilience and flips off the cumulated toner powder as shown in FIG. 2C, and then the cleaning blade 103 returns to an original position as shown in FIG. 2D. The cleaning blade 103 removes the residual toner while repeatedly producing the aforementioned action due to a so-called stick-slip phenomenon.
Therefore, the conventional cleaning system is associated with a problem that surrounding areas of the cleaning blade 103 are apt to be contaminated with the toner powder scattered around by the stick-slip phenomenon. Furthermore, since great pressure is applied to the cleaning blade 103, the tip end of the cleaning blade 103 tends to wear or be cut away. The outer surface of the endless belt 101 with which the cleaning blade 103 is forced in tight contact is likely to wear or be abraded. In addition, the pressing cleaning blade 103 is prone to cause meandering of the endless belt 101.
If the endless belt 101 exerts too large a friction force on the cleaning blade 103, the tip end of the cleaning blade 103 would occasionally become bent in an opposite direction as shown by broken lines in FIG. 3. When the tip end of the cleaning blade 103 is bent in the opposite direction as illustrated, the cleaning blade 103. will not be able to remove the toner. Typically, a slip agent 104 made of fine spherical plastic particles is applied to the outer surface of the endless belt 101 as shown in FIG. 4 in the conventional cleaning system. The slip agent 104 serves to prevent such backward bending of the cleaning blade 103 as mentioned above (FIG. 3). In addition, fine particles of an external additive 106 made of silica and magnetite are attached to an outer surface of each toner particle 105.
Each particle of the slip agent 104 is approximately 0.3 micrometers in diameter while each particle of the external additive 106 has a diameter smaller than that of the slip agent 104. Since the outer surface of the rotating body 102, against which the cleaning blade 103 forces the endless belt 101, has a surface roughness of approximately 50 micrometers, the particles of both the slip agent 104 and the external additive 106 pass through a gap between the rotating body 102 and the cleaning blade 103.
The particles of the slip agent 104 and the external additive 106 passing between the rotating body 102 and the cleaning blade 103 act as abrasive material, which accelerates wear of the endless belt 101 against which the cleaning blade 103 is tightly pressed. In a case where the cleaning system is used for cleaning a photosensitive drum, those particles of the slip agent 104 and the external additive 106 applied to each toner particle 105 which have passed between the photosensitive drum and the tip end of the cleaning blade 103 would adhere to a charging wire for electrostatically charging the photosensitive drum, thereby causing uneven tones of a printed image.
An example of a cleaning system employing a cleaning blade is found in Japanese Patent Application Publication No. 1992-362680. The Publication discloses an arrangement for preventing backward bending of the cleaning blade which is pressed against an image transfer belt with the aid of an elastic reinforcing plate which has higher stiffness than the cleaning blade and is disposed in contact with the cleaning blade on a rear side thereof.
Another example of a cleaning system employing a cleaning blade is found in Japanese Patent Application Publication No. 2002-148958. This Publication also discloses an arrangement for preventing deformation (backward bending) of the cleaning blade. In this arrangement, an image transfer belt has a double-layer structure including a base layer having high flexibility and a surface layer formed by heat-bonding a plastic film to the base layer to provide improved lubricity between the cleaning blade and the image transfer belt.
The aforementioned prior art arrangements disclosed in Japanese Patent Application Publication Nos. 1992-362680 and 2002-148958 are approaches to preventing backward bending of the cleaning blade. Accordingly, neither of these arrangements prevents the aforementioned problems of the prior art, such as contamination of the surrounding areas of the cleaning blade 103 by the toner powder scraped off and scattered around, wear or cutting of the tip end of the cleaning blade 103, wear of the endless belt 101 and uneven tones of a printed image caused by those particles of the slip agent 104 and the external additive 106 which have passed between the photosensitive drum and the tip end of the cleaning blade 103.